1. Field of the Invention
The present invention relates to a reflective active matrix substrate and a counter substrate which do not use a backlight, a method for producing the same, and a liquid crystal display device using the same.
2. Description of the Related Art
In recent years, the application of a liquid crystal display device to a word processor, a lap-top personal computer, a miniaturized TV, etc. has been rapidly developed. In particular, a reflective liquid crystal display device, which performs a display using the reflection of light incident from outside, consumes low electric power since it is not necessary to use a backlight, and can be made thin and light-weight. For this reason, much attention is paid to the reflective liquid crystal display device. Conventionally, a twisted nematic (TN) system and a super-twisted nematic (STN) system are employed in the reflective liquid crystal display device.
However, according to these systems, half of the optical strength of natural light is not used because of a linear polarizer provided in the liquid crystal display device, so that a display becomes dark. In view of this drawback, a display mode, in which all of the optical strength of natural light can effectively be used, has been proposed. One example for this is a phase transition type guest-host system (D. L. White and G. N. Taylor. J. Appl. Phys. 45 4718 (1974)).
A liquid crystal display device using a display mode of the phase transition type guest-host system employs cholesteric-nematic phase transition phenomenon caused by an electrical field, and does not require a polarizing plate such as a linear polarizer. A reflective multi-color display obtained by combining this type of liquid crystal display device and a micro-color filter has also been proposed (Tatsuo Uchida etc. Proceedings of the SID Vol. 29/2 157 (1988)).
In order to obtain a brighter display in a display mode which does not require a polarizing plate, the strength of light, which is incident upon a display screen at any incidence angle and which is scattered in a vertical direction thereto, should be increased. For this purpose, it is required to manufacture a reflective plate with regulated optimum reflection characteristics by regulating the reflection characteristics of the reflective plate. In literature proposing the above-mentioned reflective multi-color display, a reflective plate obtained by regulating a configuration of unevenness formed on a surface of an insulating glass substrate and forming a metallic thin film such as a film made of Ag on the glass substrate with the unevenness is described.
However, in the above-mentioned reflective plate, unevenness (convex and concave portions) is formed by scratching the surface of the glass substrate with a polishing agent. Thus, uniform unevenness cannot be formed, decreasing reproducibility of the configuration of unevenness. In addition, when the glass substrate thus produced is used, a reflective liquid crystal display device having satisfactory reflection characteristics cannot stably be provided.
For the purpose of overcoming the abovementioned drawback, the applicant of the present invention has proposed the following reflective plate (Japanese Patent Application No. 3-4573).
A photosensitive resin is coated onto an insulating substrate, and the substrate thus obtained is patterned. Then, the substrate is heat-treated so that an upper edge of the pattern is made round. After that, a polymer resin is allowed to flow onto the insulating substrate with the pattern to form a polymer resin film thereon. A reflective thin film having an optical reflecting function is formed on the polymer resin film, whereby a reflective plate is obtained.
Since the reflective plate thus produced has a reflective thin film in which the surfaces of the convex and concave portions are smooth, so that multiple reflection is not likely to be caused and a bright display can be obtained. However, the reflection thin film formed on a portion of the insulating substrate, under which no pattern is provided, sometimes has a flat shape. In some cases, there is a problem in that reflected light which has dependence on a wavelength is generated to cause interference color (i.e., color generated due to interference light).